Continued use of serum alpha-fetoprotein (AFP) and human chorionic gonadotropin (HCG) measurements have aided the monitoring of therapy in patients with hepatocellular carcinoma (HC) and testicular germ cell tumors. Measurement of these two markers along with the simultaneous quantitation of carcinoembryonic antigen (both CEA and CEA-S) in patients being evaluated for gastrointestinal cancers have indicated in a preliminary fashion that more than one marker elevation was found in gastric and pancreatic cancer, but not in patients with benign disease of the stomach and pancreas. Serum AFP is being quantitated to follow the development of HC in monkeys treated with carcinogens and in mice with a high incidence of spontaneous HC development.